1. Field of the Invention
The present invention relates to a method of preparing monodisperse polymer particles, to the said monodisperse polymer particles as such, and to applications of the said polymer particles thus prepared.
2. Background of the Invention
Cyclodextrins (further in the text referred to as xe2x80x9cCDsxe2x80x9d) are, from a structural point of view, well known cyclic species that can solubilize hydrophobic compounds in aqueous media. The solubilization is effected by complexation of water-insoluble species within the hydrophobic cavity of the CD. The outer hydrophilic surface then interacts with water in order to maintain the solubilization of the complex. In literature several authors report on use of CDs in copolymerisation of hydrophobic monomers with water soluble monomers as has e.g. been disclosed in following references.
Cyclodextrins in Polymer Synthesis: Influence of Acrylate Side Groups on the Initial Rate of Radical Polymerisation of Various Acrylate/Methylated xcex2-cyclodextrin Complexes in Water. Bernhardt, Stefan; Gloeckner, Patrick; Theis, Alexander; Ritter, Helmut, Macromolecules (2001), 34(6), 1647-1649.
Cyclodextrins in polymer synthesis: polymerization of methyl methacrylate under atom-transfer conditions (ATRP) in aqueous solution. Storsberg, Joachim; Hartenstein, Markus; Mxc3xcller, Axel H. E.; Ritter, Helmut. Macromol. Rapid Commun. (2000), 21(18), 1342-1346.
Cyclodextrins in polymer synthesis: free radical polymerization of methylated xcex2-cyclodextrin complexes of methyl methacrylate and styrene, controlled by dodecane thiol as the chain-transfer agent in aqueous medium. Glxc3x6ckner, Patrick; Ritter, Helmut, Macromol. Chem. Phys. (2000), 201(17), 2455-2457.
Carbohydrate/Monomer Complexes in Aqueous Polymerisations: Methylated-xcex2-cyclodextrin Mediated Aqueous Polymerisation of Hydrophobic Methacrylic Monomers. Madison, Phillip H.; Long, Timothy E, Biomacromolecules (2000), 1(4), 615-621.
Methylated-xcex2-cyclodextrin mediated aqueous polymerization of hydrophobic methacrylic monomers. Madison, Phillip H.; Long, Timothy E., Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) (2000), 41(2), 1836-1837.
Cyclodextrins in Polymer Synthesis: Free Radical Copolymerization of Methylated xcex2-Cyclodextrin Complexes of Hydrophobic Monomers with N-Isopropylacrylamide in Aqueous Medium. Casper, Patrick; Glxc3x6ckner, Patrick; Ritter, Helmut. Macromolecules (2000), 33(12), 4361-4364.
Cyclodextrins in polymer synthesis: free radical polymerisation of cyclodextrin host-guest complexes of methyl methacrylate or styrene from homogeneous aqueous solution. Storsberg, Joachim; Ritter, Helmut. Macromol. Rapid Commun. (2000), 21(5), 236-241.
Manufacture of polymers by radical polymerization of water-insoluble monomers in aqueous medium. Schornick, Gunnar; Kistenmacher, Axel; Ritter, Helmut; Jeromin, Julia; Noll, Olaf; Born, Markus. (BASF A. -G., Germany) in DE-OS 19533269 A1.
Reports related with use of CDs in heterogeneous reactions, such as emulsion polymerizations or dispersion polymerizations, are scarce. A few references are enclosed below.
Rimmer e.g. (references given hereinafter) describes use of cyclodextrins in a batch-wise emulsion polymerization: in some cases he makes use, besides cyclodextrin, of an anionic surfactant (as e.g. Dowfax 2A1). In other heterogeneous polymerizations where cyclodextrins are used, such as patents from Willy Lau et al. or Reinhold Leyrer et al., considerable amounts of anionic surfactants are always used, such as sodium dodecyl sulphate, dodecyl benzene sulphonic acid sodium salt, Rhodapex CO-436 (sodium salt of sulphated polyethoxynonylphenol), Triton XN-45S or Dow fax (sulphonated alkyl diphenyl oxide). From the present invention it will become clear that a batch-wise procedure and presence of additional anionic surfactants are undesirable in view of the objects to be attained. A few references where this has not been taken into account are:
Cyclodextrins in the emulsion polymerization of vinyl monomers. Rimmer, S., Macromol. Symp. (2000), 150 (Polymers in Dispersed Media), p. 149-154.
Emulsion polymerizations in the presence of xcex2-cyclodextrin. Rimmer, S.; Tattersall, P. I. Polymer (1999), 40(24), 6673-6677.
Preparation of polymers by aqueous polymerization. Lau, Willie (Rohm and Haas Company, USA); EP-A 0 710 675.
Preparation of fluorinated polymers. Parker, Hsing-Yeh; Lau, Willie; Rosenlind, Erik Sigurd (Rohm and Haas Company, USA); EP-A 0 890 592.
Preparing polymers by emulsion polymerization in the presence of compounds capable of forming a supermolecular structure. Leyrer, Reinhold; Mathauer, Klemens; Roser, Joachim; Wildburg, Gerald; Haunschild, Alexander (BASF A. -G., Germany); EP-A 0 780 401.
Moreover those reports are all related with use of CDs in heterogeneous reactions, wherein polymer particles having a heterogeneous particle size distribution are obtained, whereas use of polymer particles having a narrow particle size distribution are highly desired.
It is an object of the present invention to make use of cyclodextrin in heterogeneous polymerization reactions, such as emulsion polymerizations or dispersions polymerizations, in order to obtain a more narrow particle size distribution.
It is furthermore an object of the present invention to provide a method in order to perform the cyclodextrin mediated heterogeneous polymerization reaction, thereby getting a much better colloidal stability of particles having a more narrow particle size distribution.
Moreover it is an object of the present invention to perform the cyclodextrin mediated heterogeneous polymerization in order to obtain no nucleation from different types of micelles.
Still another object of the present invention is to give the formed latex additional stability.
It is an ultimate object of the present invention to get monodisperse polymer particles which are applicable in quite a lot of diverse well-known and novel applications in order to broaden the scope of applicability.
Further advantages and embodiments of the present invention will become apparent from the description following hereinafter.
As a result of our investigations a method has been described of preparing monodisperse polymer particles by free radical polymerization or copolymerization of hydrophobic monomers in a water-based system in the presence of cyclodextrin, characterized in that said free radical polymerization is performed with semi-continuous addition of monomer, wherein said monomer is absent before initiating polymerization, and in that a total solid contents of less than 30% by weight is present in said water-based system. Monodisperse polymer particles thus prepared have been shown to be very suitable for use in many applications as e.g. in inks or toners, in photonic crystal films, in thermal printing plates for computer-to-plate or computer-to-press applications, in inkjet media, in displays, in photographic films, or as spacing agent.